Packaging and wrapping of products using foil is widely used in many industries. Such packed or wrapped products could be for the building industry and range from building materials such as plaster plates to glass or mineral wool. One of the primary requirements for the packaging of such products is naturally that the material wrapped around the products serves to protect the products until it is purposely broken.
When wrapping insulation materials, such as glass or mineral wool, the foil is often used as a mean for maintaining a compression of normally a stack of insulation objects. The insulation objects are compressed and then wrapped in un-stretched or stretched foil, which is joined by welding. The welding is made by a welding assembly comprising two pairs of resilient jaws, between which a knife for cutting the foil is placed. Further, between the knife and the resilient jaws two pairs of welding beams for welding the foil are positioned. When the objects to be packed have been wrapped in the foil, the foil is stretched and held between the resilient jaws and at the same time clamped between the welding beams. Hereafter the foil is cut and welded at the same time.
To reduce the production costs, it is desired to reduce the amount of foil used per package. This is done by using thinner foils in the existing production facilities. However, using thinner foil is encumbered with one major problem. Regardless of the foil thickness, the thermal stress applied to the stretched foil during welding will release the tension present in the foil. This will lead the foil to creep and consequently lead to a thinning of the foil between the resilient jaws and the welding beam. When using thin foils, the thinning can reduce the yield strength of the foil below the required level or be so severe that the foil is reduced to only thin threads. There is therefore a great risk that the packaging process fails or that the finished package is torn or breaks open unintentionally.